1. Field of the Invention
The present invention relates to a bead cord which is embedded in a bead portion of a pneumatic tire. More particularly, the present invention relates to a method and an apparatus of manufacturing an annular concentric stranded bead cord having one sheath layer or a plurality of sheath layers formed by continuingly spirally winding a lateral wire along an annular core.
2. Description of the Related Art
An annular concentric stranded bead cord is used in tires of various types of vehicles.
As shown in FIGS. 9A and 9B, an annular concentric stranded bead cord includes a sheath layer of lateral wire 2 provided upon an annular core 1. It is manufactured by continuingly spirally winding the lateral wire 2 along the annular core 1 as a result of passing the lateral wire 2 to the inner side of a ring of the annular core 1 from the outer side of the annular core 1, and, then, passing them again to the inner side of the ring from the outer side of the ring.
The following methods have hitherto been disclosed as methods of manufacturing an annular concentric stranded bead cord.
First, Japanese Patent No. 3499261 discloses a method of manufacturing a bead cord using, as a lateral wire, a wire previously reformed so as to have at least twice the diameter of an annular core, when the lateral wire is spirally wound upon the annular core. When a bead cord manufactured by this method is used in a tire, a person has a feeling that elasticity is high, and a gripping force, turning force, and responsiveness are increased.
Japanese Unexamined Patent Application Publication No. 2001-47169 discloses another method. As illustrated in FIG. 10, in the method, an end of a lateral wire 2 is temporarily secured to an annular core 1 by a chucking mechanism. While rotating the annular core 1 in a peripheral direction, a reel 3 is revolved to an inner side and an outer side of the annular core 1. By this, the lateral wire 2 is spirally wound upon the outer periphery of the annular core 1. The chucking mechanism is unchucked from the annular core 1 before the end of the lateral wire 2 that is temporarily secured to the annular core 1 overlaps the position of revolution of the reel 3. Accordingly, interference between the chucking mechanism and the reel 3 is prevented from occurring to continue the revolution of the reel 3. This method makes it possible to alternately perform an S winding and a Z winding a plurality of times, so that problems, such as tangling and twisting of the lateral wire 2, are prevented from occurring. As a result, it is possible to considerably increase the productivity and the quality of the bead cord.
Japanese Unexamined Patent Application Publication No. 2004-98640 discloses still another method of manufacturing a bead cord. In the method, an end of a lateral wire is either entangled upon an annular core without securing the lateral wire or temporarily secured to the annular core, and allowed to rotate freely. A plane movement of a reel (for winding as a result of bending to a diameter that is less than that of the annular core), a vertical operation of the annular core, and rotation of the annular core are combined to entangle the lateral wire upon the annular core by bending stress of a steel wire, so that twisting stress is prevented from being generated for manufacturing the bead cord.
WO2004/018187A1 discloses still another method of manufacturing a bead cord. In the method, as illustrated in FIG. 12, a reel 3, upon which a lateral wire 2 is wound, is secured to a predetermined location. A driving unit 5, which rotates an annular core 1 in a peripheral direction, is made to reciprocate in a straight line along the surface of the annular core 1. At an end of a reciprocation period, the reel 3 is positioned at an outer side of a ring of the annular core 1 (as indicated by a solid line in FIG. 12). At the other end of the reciprocation period, the reel 3 is positioned in an inner side of the ring of the annular core 1 (as indicated by broken lines in FIG. 12). At the inner and outer sides of the ring of the annular core 1, the reel 3 is transferred so as to traverse the surface of the annular core 1, whereby the lateral wire 2, which is drawn out from the reel 3, is continuingly spirally wound upon the annular core 1, to manufacture the bead cord.
Japanese Unexamined Patent Application Publication No. 2006-110981 discloses still another method of manufacturing a bead cord. As illustrated in FIGS. 13 and 14, in the method, a reel 3 is made to, at a predetermined position, reciprocate so as to traverse a surface of an annular core 1. With a clamp unit 4, which corresponds to a winding point of a lateral wire 2, being a fulcrum, the annular core 1 is made to undergo a pendulum swinging movement. By this, the distance from the reel 3 to the winding point of the lateral wire 2 is maintained at a substantially constant value, so that, during winding, the lateral wire 2, which is drawn out from the reel 3, is not loosened. As a result, the lateral wire 2 is wound upon the annular core 1 at a constant tension to manufacture the bead cord.
The stability of the form of a bead cord is the most important for the quality of the bead cord. The bead cords manufactured by the methods according to the aforementioned patent documents have the following problems.
As regards the bead cord manufactured by the method disclosed in Japanese Patent No. 3499261, a lateral wire, which is previously formed so as to have a diameter that is at least twice that of the annular core for the purpose of increasing the elasticity of a tire, is wound. Therefore, it is difficult to achieve automation, and there are many factors that increase costs. In addition, when the coil diameter of the lateral wire, which is wound upon the annular core, is large, it is troublesome to wind the lateral wire by hand. Further, since the lateral wire is previously modified, resistance is increased when the lateral wire is drawn out, thereby causing winding problems. Still further, when the lateral wire is wound upon the annular core after taking up the lateral wire by the reel, the winding of the lateral wire becomes loose unless a certain tension that is greater than or equal to a certain value is constantly applied. Even with a small tension, the annular core tends to become deformed, thereby adversely affecting windability.
As regards the method disclosed in Japanese Unexamined Patent Application Publication No. 2001-47169, an end of the lateral wire is temporarily secured to the annular core by the chucking mechanism, and the reel is revolved to the inner side and the outer side of the annular core while the annular core rotates in the peripheral direction. Therefore, the angle at which the lateral wire is wound upon the annular core varies greatly. In addition, there are many unnecessary movements, and the apparatus, itself, becomes massive.
In addition, as regards the method disclosed in Japanese Unexamined Patent Application Publication No. 2001-47169, as shown conceptually in FIG. 10, the reel 3 revolves to the inner side and the outer side of the annular core 1. Therefore, the lateral wire 2 is wound upon the annular core 1 while a winding deviation angle βS changes from 0 degrees (shown in FIG. 11A), at which the lateral wire 2 and the annular core 1 are parallel to each other, to approximately 50 degrees (shown in FIG. 11B), at which the reel 3 is situated away from the annular core 1. A twist angle β of a bead core used in a generally commercially available tire is from 3.5 to 5.5 degrees in a 1+m twist structure for a two-wheeled vehicle. A twist angle β is approximately 7 degrees in a 1+m+n twist structure for a passenger vehicle/light truck. Therefore, as the difference between the winding deviation angle βS and the twist angle β becomes large as mentioned above, the state of arrangement of the lateral wire 2 that is being continuingly wound tends to become disturbed, thereby resulting in poor cord formability.
Further, as regards the method disclosed in Japanese Unexamined Patent Application Publication No. 2001-47169 in which the reel 3 revolves to the inner side and the outer side of the annular core 1, since the reel 3 moves along a circular path, its movement is redundant, thereby requiring a long period of time until the winding ends. In addition, since the lateral wire 2 is wound as a result of applying a certain tension, the annular core 1 is pulled in the peripheral direction. Therefore, the annular core 1 tends to meander, resulting in poor windability.
Next, as regards the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-98640, the annular core is placed horizontally, and moves in a complicated manner. Therefore, similarly to the case disclosed in Japanese Unexamined Patent Application Publication No. 2001-47169, the winding deviation angle βS varies considerably, thereby resulting in unstable windability. In addition, the horizontal movement of the reel is reversed after one interval, and takes twice the time. As a result, twice the time is required to finish manufacturing the bead cord. Unless the movement of the annular core, which becomes the base during the winding, is maximally limited, the windability tends to become unstable. In particular, since the annular core is placed in a gravitational direction and is moved vertically with respect to the gravitational direction, and the reel, upon which the lateral wire is wound, is continuously moved, the windability is poor. As regards the method disclosed in WO2004/018187A1 illustrated in FIG. 12, the reel 3 is secured to a predetermined position, and the driving unit 5, itself, reciprocates in a straight line. By this, the annular core 1 moves close to and away from the reel 3 so that the reel 3 moves to the inner side and the outer side of the ring of the annular core 1. Therefore, when the annular core 1 approaches the reel 3, the lateral wire 2 is pushed in a direction in which the lateral wire 2 is loosened. In contrast, when the annular core 1 moves away from the reel 3, the lateral wire 2 is pulled. Therefore, the winding point where the lateral wire 2 is wound with respect to the annular core 1 is displaced greatly as the annular core 1 moves. Consequently, it is difficult to arrange the lateral wire 2, as a result of which the arrangement of the lateral wire 2 tends to be disturbed.
As regards the method disclosed in Japanese Unexamined Patent Application Publication No. 2006-110981 illustrated in FIGS. 13 and 14, the annular core 1, which rotates in the peripheral direction, undergoes pendulum swinging movement with the clamp unit 4 (which is the winding point of the lateral wire 2) serving as a fulcrum. Therefore, the entire apparatus becomes large, the rotation of the annular core 1 in the peripheral direction becomes unstable, and the arrangement of the lateral wire tends to become disturbed.